I'm on the other end of this - I have a friend who calls me about once a week, and often when she calls I'm either not home or I'm not able to talk right then (watching a movie with DH, or playing World of Warcraft with a group of other people). I don't want to inconvenience my DH or a group of 39 online friends for a chat we could do anytime, so I end up saying "Can I call you back later?" a lot. Sometimes I do, and sometimes I don't. My friend and I really don't have all that much in common anymore, and we live across the country from each other, so I feel kind of silly calling "just to talk" when there's really nothing to talk about.
I wouldn't be surprised if she's feeling the same way you are, and wondering whether I still want to be her friend. I do, but I'm not a person for long phone conversations. I'm happy to see her whenever we're both in the same state, but I'm also okay going for months or even years without communicating much. I'm like this with almost everybody (right now, most of my high school and college friends are spread out across the country, and I haven't made a ton of local friends in the meantime). Some people are comfortable with it and some aren't - but we'll all catch up when we see each other the next time.